Weird DNS problem...

We have an intranet located internally on a windows 2003 / iis6 server - DNS handled internally on another windows 2003 server.

The intranet, amongst other functions, hosts a ecommerce store I wrote that sells nike apparel embroidered with our company logo. Up until recently, it would send an email to payroll and the cost would be deducted from the employees paycheck.

lets say this store is located at http://mydomain.com (only available internally)

Now, we've been told by the accountants that we can no longer auto deduct from payroll and the employee needs to pay with a credit card or cash.

So i went to thawte.com and ordered an SSL cert to be on the safe side (even though the CC gateway is secure) and they told me i need to drop the .com from the domain name

Not wanting to mess with a system thats perfectly functional, i created another DNS entry that just points to mydomain (no .com) and left the old one in there.

so they would go to http://mydomain

On my Mac (OS X 10.6) i can hit either one just fine

On Windows XP / Windows XP Embedded or Windows 7 (the vast majority of the pc's on our network) http://mydomain - returns nothing http://mydomain.com still works https://mydomain.com works but says the cert is invalid (as it should, it was issued to mydomain - not mydomain.com)

my question is: why does it work on my Mac and not on a Windows PC (i get dhcp and dns just like any other pc on the network) and will removing the .com one from the DNS server resolve this?

I've done all the usual attempts - ipconfig /flushdns, ipconfig /renew and release

even going so far as to stop and restart DNS client on my Windows 7 box; rebooting and shutting down - adding a regedit entry something along the lines of SecureResponses and rebooting

nothing works... I think its the .com and the not conflicting in DNS but i'm not sure - and why not on OS X

We're closed on sunday and i'm going to remote in and see what happens if i remove the .com from DNS but any other ideas?

-Mario